1. Field of the Invention
The present invention relates to a channel management method and a channel selection method for a wireless node in a wireless ad-hoc network, and more particularly, to a method in which a wireless node changes or resets a reception interface channel according to a possibility in consideration of channel distribution of surrounding wireless nodes.
2. Discussion of Related Art
In general, a wireless node of a wireless ad-hoc network uses single-channel single-interface. In a wireless ad-hoc network based on single-channel single-interface, all wireless nodes use the same channel. Therefore, when a wireless node transmits data, neighbor nodes, i.e., other wireless nodes adjacent to the wireless node, cannot transmit data, as illustrated in FIG. 1. Here, the term “neighbor node” denotes another wireless node located within the transmission range of one wireless node, and the term “transmission range” denotes coverage within one hop of a wireless node.
To solve the problem and efficiently use wireless resources, wireless ad-hoc networks based on multi-channel have been suggested as shown in FIGS. 2 and 3. FIG. 2 illustrates a wireless ad-hoc network based on multi-channel single-interface, and FIG. 3 illustrates a wireless ad-hoc network based on multi-channel multi-interface.
When a wireless node transmits data in a wireless ad-hoc network based on multi-channel single-interface, neighbor nodes can transmit data through other channels. However, the wireless node uses a single interface and thus cannot simultaneously perform a transmitting operation and a receiving operation, as illustrated in FIG. 2.
In a wireless ad-hoc network based on multi-channel multi-interface, a wireless node and neighbor nodes can simultaneously transmit data and can also simultaneously perform a receiving operation as well as a transmitting operation. Therefore, it is possible to efficiently use wireless resources using multi-channel multi-interface.
FIG. 4 illustrates the structure of a wireless node using multi-channel multi-interface. Between an Internet Protocol (IP) layer 401 and a Media Access Control (MAC) layer 404, a channel control layer 400 controls the channel of each interface. In addition, a data queue 406 is divided into several channel queues 407, thereby classifying data of respective channels. A fixed interface 402 in charge of a reception interface channel receives data through an interface whose channel is not frequently changed. A switchable interface 403 in charge of a transmission interface channel transmits data through an interface whose channel is frequently changed. In other words, when there is data to be transmitted, the wireless node changes the channel of the switchable interface 403, i.e., the transmission interface channel, to the channel of the fixed interface 402, i.e., the reception interface channel, of a neighbor node corresponding to a next hop, and then transmits the data through the switchable interface 403.
FIG. 5 illustrates a data transfer process in a wireless ad-hoc network based on multi-channel multi-interface. When a first node NODE_1 transmits data to a third node NODE_3, the data must pass through a second node NODE_2 to be transmitted to the third node NODE_3. The first node NODE_1 changes the channel of its switchable interface to a channel CH_3 of a fixed interface of the second node NODE_2 (step 500), and then transmits the data to the second node NODE_2 (step 502). The second node NODE_2 receiving the data from the first node NODE_1 changes the channel of its switchable interface to a channel CH_2 of a fixed interface of the third node NODE_3 (step 504), and then transmits the data to the third node NODE_3 (step 506).
Meanwhile, to efficiently use a channel in an ad-hoc network environment based on multi-channel multi-interface, the number of wireless nodes using each channel must be similar to each other. To this end, each wireless node determines a channel according to the following method. Each wireless node selects and sets its own reception interface channel so that channels are evenly distributed within its interference range. More specifically, each wireless node collects information on channel distribution within its interference range and then determines the least distributed channel as its own reception interface channel. Here, the term “interference range” denotes coverage within two hops of a wireless node.
Operation of each wireless node according to the above-described data transmission technique and channel selection method is summarized as follows. Each wireless node periodically broadcasts a Hello message. In addition, the wireless node updates its own reception interface channel on the basis of a Hello message received from a neighbor node so that channels are evenly distributed within its interference range. Further, when the wireless node transmits data, it changes its transmission interface channel to the reception interface channel of the next hop and then transmits the data to the next hop.
Meanwhile, to perform the above-described data transmission, the wireless node must know the channel of the fixed interface of a neighbor node, i.e., a node one-hop away from the wireless node. In addition, to perform the above-described conventional channel selection method, the wireless node must know the channels of the fixed interfaces of a neighbor node and a wireless node two hops away from the wireless node. For example, a method uses a Hello message to find the channels of the fixed interfaces of a neighbor node and a wireless node two hops away. According to the method, each wireless node periodically broadcasts a Hello message including channel information through all channels. The channel information includes information on the reception interface channel of a wireless node itself and information on the reception interface channel of a neighbor node obtained from the Hello message.
FIG. 6 illustrates a problem of the conventional channel selection method. In FIG. 6, small circles and large circles denote transmission ranges and interference ranges of wireless nodes 601, 602 and 603, respectively.
The wireless node 601, which uses channel 1 as the channel of its fixed interface in a state illustrated in the upper left part of FIG. 6, changes the channel of the fixed interface to channel 2 because the number of channel 2 is the least within its interference range. Through this channel changing process 604, respective channels are distributed as illustrated in the upper right part of FIG. 6.
The wireless node 602, which uses channel 2 as the channel of its fixed interface in a state illustrated in the upper right part of FIG. 6, changes the channel of the fixed interface to channel 3 because the number of channel 3 becomes the least within its interference range due to the channel changing process 604. Through this channel changing process 605, the respective channels are distributed as illustrated in the lower right part of FIG. 6.
The wireless node 603, which uses channel 3 as the channel of its fixed interface in a state illustrated in the lower right part of FIG. 6, changes the channel of the fixed interface to channel 2 because the number of channel 2 becomes the least within its interference range due to the channel changing process 605. Through this channel changing process 606, the respective channels are distributed as illustrated in the lower left part of FIG. 6.
The wireless node 601, which uses channel 2 as the channel of its fixed interface in a state illustrated in the lower left part of FIG. 6, changes the channel of the fixed interface to channel 1 because the number of channel 1 becomes the least within its interference range due to the channel changing process 606. Through this channel changing process 607, the respective channels are finally distributed in the original state illustrated in the upper left part of FIG. 6.
In other words, according to the conventional channel selection method, an infinite loop may be generated in order of the upper left state, the upper right state, the lower right state, the lower left state and the upper left state again, as illustrated in FIG. 6, and thus respective wireless nodes frequently change their channel. The frequent channel change of a neighbor node causes a wireless node transmitting data to frequently change the transmission interface channel of the wireless node, which results in data transmission delay and network performance deterioration.